Dr MacRae was described as being “paranoid” about the plant which is so destructive it can make it impossible to sell your home and can cost upwards of £20,000 to treat.

The plant, which was introduced to Britain in Victorian times, can grow as much as nine feet in just ten weeks and can cause untold damage to the foundations of buildings.

General view of the house on Bryan Budd Close, where the bodies of Kenneth, 52, and Jane McRae, 55, were discovered (Newsteam/ SWNS)

He became convinced that the plant was spreading from the golf course behind his home in Rowley Regis, West Midlands and claimed to be locked in legal battles with the owners of the land.

But West Midlands Coroner Robin Balmain was told there was no evidence of knotweed in his plot and there had been no legal battle with the golf club.

In his suicide note, Dr McRae wrote: “I believe I was not an evil man, until the balance of my mind was disturbed by the fact there is a patch of Japanese Knotweed which has been growing over our boundary fence on the Rowley Regis Golf Course.”

He added: “Jane and I were a very private couple, we chose to have no real friends, just enjoying each other.

“But the despair has got so bad that today I have killed her, as I did not want her to be alone without an income when I killed myself.”

A police investigation found she may have lain dead in bed on the second floor of the three-storey house for up to a week.

The couple were found when police broke into their home after worried colleagues of Dr McRae raised concerns after he failed to turn up for work.

Mr Balmain said: “This is clearly a tragedy. They appeared for whatever reason to keep themselves to themselves, they were perfectly entitled to do that.

“The impression is Mr McRae was possibly becoming paranoid, there is no direct evidence of that of course.

“He had got a responsible job as a lab technician, his own home free from mortgage. It appears he became obsessed with Japanese Knotweed in the vicinity, which was not even on his property.

“It is perfectly clear he chose to kill his wife. It is difficult to understand what was going on in Mr McRae's mind. For whatever reason, he killed his wife and then himself.”

The court heard the couple were estranged from their family and had not spoken to their adopted son for over a decade.